The important relationship of diet and nutrition in the development of cancer has become well known through various research efforts. Laboratory studies have shown cancer inhibitory functions for several natural and synthetic nutrients in various models, which have been corroborated by human epidemiologic studies of nutrient intake, tissue levels and cancer incidence. Vitamin A, vitamin E, beta-carotene and selenium have been strongly implicated for their cancer preventive potential, with evidence for the former three substances warranting clinical trials of their efficacy. In addition, the roles of other nutrients in cancer cause and prevention (e.g., dietary fats and fiber) require further investigation. The objectives of this cooperative project with the National Public Health Institute of Finland are: 1) to determine if supplementation with beta-carotene, vitamin E, or both, is effective in preventing lung cancer in smokers; 2) to assess the role of dietary selenium, vitamins A, E, and C, and fats in breast cancer development; 3) to evaluate the relationship between various levels of nutrient intake and subsequent cancer risk. The project includes three studies. The first, a beta-carotene, vitamin E lung cancer intervention trial, is a five-year, 2x2 factorial randomized trial of daily beta-carotene (20 mg orally) or alpha tocopherol (100 mg orally) among cigarette smokers. Any deduction of lung cancer incidence in the treatment groups will be measured. The second is a breast cancer case-control study of selenium, vitamins A, E, C fats and other nutrients, using both benign breast disease and neighborhood controls. The importance of these nutrients in breast cancer development will be assessed. Finally, the dietary survey study will assess previously collected dietary history information for a subgroup having developed cancer out of an original population cohort.